Purpose: The moving rectangle method is used to disentangle the contributions of rectangularization and
life span extension to the increase in life expectancy. It requires the choice of an endpoint of the survival
curve that approaches the maximum age at death. We examined the effect of choosing different end
points on the outcomes of this method.
Methods: For five developed countries, survival curves from age 50 years were constructed per calendar
year from 1922 onward. Survival values of 0.1, 0.01, and 0.001 were chosen as end points of the survival
curve, and the contributions of rectangularization and life span extension to the increase in life expectancy
were calculated using the moving rectangle method.
Results: The choice of different survival values as end points profoundly influenced the estimated contributions
of rectangularization and life span extension to the increase in life expectancy. When choosing
0.001, rectangularization contributed most years, whereas when choosing 0.1, life span extension
contributed most years.
Conclusions: When the moving rectangle method is used to estimate the contributions of rectangularization
and life span extension to the increase in life expectancy, its outcomes depend on the choice of the
endpoint of the survival curve.